1. Field of the Invention
This invention relates to a toner used in recording processes such as electrophotography, electrostatic recording, electrostatic printing, toner jet recording and so forth, and a process for producing the toner.
2. Related Background Art
Image forming apparatus making use of electrophotographic techniques, such as copying machines and laser beam printers, have become functionally rich in variety, where toner images to be obtained are required to be formed in a higher minuteness and a higher image quality, and toners suited therefor are used.
For example, Japanese Patent Publication No. S51-23354 discloses a toner composed of a vinyl polymer having appropriately been cross-linked by the addition of a cross-linking agent and a molecular weight modifier, and further a large number of toners are proposed which are of a blend type in which, in the vinyl polymer, Tg, molecular weight and gel content are specified in combination.
Such a toner having a cross-linked vinyl polymer or a gel content exhibits a superior effect in respect of anti-offset properties. However, in incorporating these, where this cross-linked vinyl polymer is used as a toner raw material, the internal friction in the polymer is very large in the step of melt kneading when the toner is produced, so that a large shear force is applied to the polymer. This causes cut of molecular chains in many cases to cause a decrease in melt viscosity and may adversely affect the anti-offset properties.
Japanese Patent Application Laid-open Nos. S63-214760, S63-217362, S63-217363 and S63-217364 disclose that a polymer has molecular weight distribution divided into two groups, low-molecular weight and high-molecular weight, and a carboxyl group contained in the low-molecular weight side is allowed to react with a polyvalent metal ion to effect cross-linking (a dispersion of a metal compound is added to a solution obtained by solution polymerization, followed by heating to carry out reaction).
Japanese Patent Application Laid-open Nos. H02-168264, H02-235069, H05-173363, H05-173366 and H05-241371 also disclose toner binder compositions, and toners, in which the molecular weights, mixing ratio, and acid values and ratio thereof, of a low-molecular weight component and a high-molecular weight component in a binder resin are controlled to improve fixing performance and anti-offset properties.
Japanese Patent Application Laid-open No. S62-9256 also disclose a toner binder composition in which two kinds of vinyl polymers having different molecular weights and resin acid values are blended.
Japanese Patent Application Laid-open Nos. H03-63661, H03-63662, H03-63663 and H03-118552 disclose that a vinyl copolymer containing a carboxyl group and a vinyl copolymer containing an epoxy group are allowed to react with a metal compound to effect cross-linking.
Japanese Patent Application Laid-open Nos. H07-225491 and H08-44107 also disclose that a carboxyl group-containing resin and an epoxy resin react to form a cross-linked structure.
Japanese Patent Application Laid-open Nos. S62-194260, H06-11890, H06-222612, H07-20654, H08-44107, H09-185182, H09-244295, H09-319410, H10-87837, H10-90943, H11-43535, H11-282198, 2001-188383, 2002-148864 and 2002-189316 also disclose toner binder compositions, and toners, in which a glycidyl group-containing resin is used as a cross-linking agent, and, in a resin composition constituted of a carboxyl group-containing resin, the molecular weight distribution, viscoelasticity, gel content, acid value, epoxy value and so forth are controlled to improve fixing performance and anti-offset properties.
For these proposals having been mentioned as above, it is true that good effects are obtained in respect of the improvement in anti-offset properties, but compatibility with other components constituting the toner tends to be poor. Hence, under severe conditions at the time of high-speed printing or after long-term running, the toner may have a broad charge distribution to cause problems on image quality.
In order to prevent toners from offset, it is known to incorporate toner particles with a wax as a release agent. For example, Japanese Patent Application Laid-open Nos. S52-3304, S52-3305 and S57-52574 disclose techniques therefor.
Waxes disclosed in these are used in order to improve anti-offset properties of toners at the time of low temperature or at the time of high temperature. The waxes bring an improvement in such performance on the one hand, but on the other hand may make toners have poor anti-blocking properties or have poor developing performance.
As toners which contain two or more kinds of waxes in order to more bring out over the range of from low temperature to high temperature the effect to be brought by the addition of waxes, for example, Japanese Patent Publication No. S52-3305 and Japanese Patent Application Laid-open Nos. S58-215659, S62-100775, H04-124676, H04-299357, H04-362953 and H05-197192 disclose techniques therefor.
However, in these toners as well, none of them can satisfy every performance, and they have caused some problems. For example, toners have good high-temperature anti-offset properties and good developing performance, but are not fully satisfied with low-temperature anti-offset properties; toners have good low-temperature anti-offset properties and low-temperature fixing performance, but have a little poor anti-blocking properties and have a low developing performance; toners can not have both anti-offset properties at the time of low temperature and those at the time of high temperature simultaneously; and toners cause blotches because of toner particle coat non-uniformity due to a liberated wax component to cause image defects or cause fog on images. Also, the liberated wax may contaminate developer carrying members to bring about difficulties in development.
As also disclosed in Japanese Patent Application Laid-open Nos. H08-278657, H08-334919, H08-334920 and so forth, it is proposed to incorporate toner particles with two kinds of wax components in order to obtain toners having good low-temperature fixing performance and anti-offset properties.
In these toners making use of release agents, the temperature range where both the low-temperature fixing performance and the high-temperature anti-offset properties are achievable can be enlarged. However, it is difficult to make each wax component dispersed uniformly in toner particles, and any faulty dispersion (of wax in toner particles) may make fog occur greatly, may make developing performance poor and may cause image difficulties due to contamination of developer carrying members.
As a means for improving the dispersion of the release agent, as disclosed in Japanese Patent Application Laid-open Nos. S62-195683, H03-185458, H06-67454 and so forth, methods are proposed in which a wax component is mixed, dissolved or dispersed in a solution of a polymer.
The methods disclosed in these, however, are still insufficient, and any faulty dispersion may make fog occur greatly and may make developing performance poor.
As a further means for improving the dispersion of the release agent, as disclosed in Japanese Patent Application Laid-open Nos. S56-87051, S57-211157, S62-143060, H09-281748, H10-123753, H11-158336, H11-160911 and so forth, it is proposed that polymerization for making up a resin composition is carried out in the presence of a release agent. As also disclosed in Japanese Patent Application Laid-open No. H04-358159, it is proposed that a first wax is added at the time of polymerization for producing a synthetic resin and a second wax is added at the time of melt-kneading for obtaining toner particles.
However, in the methods disclosed in these, the release agent component and the resin dissolve completely in each other, or the release agent component disperses very finely in the resin. Hence, the releasability that is fundamentally required may be damaged, and a difficulty may come to be seen such that the toner having offset, called blobs, is accumulated on fixing assembly members (e.g., separating claws, thermistor members and so forth) to stain images, making it difficult to obtain satisfactory performance. Also, in the case when two kinds of waxes are used, it is difficult to disperse the both appropriately, and any faulty dispersion may make fog occur greatly and may make developing performance poor.
To the resin mentioned above which has been subjected to cross-linking, too, every kind of wax is added, and such attempts are also disclosed in Japanese Patent Application Laid-open Nos. H08-278663, H10-39543 and H11-24307.
However, all of these are insufficient in respect of the state of dispersion of waxes, which is still unsatisfactory in regard to high-grade running performance.